Fluid flow induced oscillating energy harvester with variable damping based upon oscillation amplitude

Abstract

An energy harvester including a stand supporting the energy harvester in a fluid flow, i.e. a stream or current; at least one bluff body extending from the stand and positioned substantially perpendicular to the fluid flow, wherein each bluff body moves relative to the stand at least in a direction perpendicular to the fluid flow, wherein sufficient flow causes oscillating movement of the bluff body; and an electrical generator coupled to the stand and coupled to at least one bluff body converting the oscillating movement to electrical power, wherein the rate of electrical power generation per movement of the bluff body (or harvesting) is varied throughout a range of amplitudes of the oscillation of the bluff body and wherein the harvesting rate of at least one amplitude of the body oscillation is greater than the harvesting rate of at least one lower amplitude of the body oscillation.

What is claimed is: 
     
       1. A fluid flow induced oscillating energy harvester comprising:
 a stand supporting the energy harvester and configured to support the energy harvester in a fluid flow; 
 at least one bluff body extending from the stand configured to be positioned substantially perpendicular to the direction of fluid flow, wherein each bluff body is mounted for movement relative to the stand at least in a direction perpendicular to the direction of fluid flow, wherein sufficient fluid flow causes an oscillating movement of the bluff body relative to the stand; 
 an electrical generator coupled to the at least one bluff body, wherein the electrical generator is configured to convert oscillating movement of the bluff body to electrical power, and wherein the electrical generator is configured such that a rate of electrical power generation per movement of the bluff body is varied throughout a range of amplitudes of the oscillation of the bluff body and wherein the rate of electrical power generation per movement of the bluff body of at least one amplitude of the oscillation of the bluff body is greater than the rate of electrical power generation per movement of the bluff body of at least one lower amplitude of the oscillation of the bluff body; and wherein the electrical generator converts oscillation of the at least one bluff body to rotation, and wherein the bluff body is extending from the stand in a cantilevered fashion. 
 
     
     
       2. The fluid flow induced oscillating energy harvester according to  claim 1  wherein a rate of rotation per oscillation displacement is higher at a higher amplitude of the oscillation of the at least one bluff body than at a lower amplitude of the oscillation of the at least one bluff body and wherein the energy harvester is configured to be suspended within the fluid flow from a structure on the surface of a river. 
     
     
       3. A fluid flow induced oscillating energy harvester comprising:
 a stand supporting the energy harvester and configured to support the energy harvester in a fluid flow; 
 at least one bluff body extending from the stand configured to be positioned substantially perpendicular to the direction of fluid flow, wherein each bluff body is mounted for movement relative to the stand at least in a direction perpendicular to the direction of fluid flow, wherein sufficient fluid flow causes an oscillating movement of the bluff body relative to the stand; 
 an electrical generator coupled to the stand and coupled to the at least one bluff body, wherein the electrical generator is configured to convert oscillating movement of the bluff body to electrical power, and wherein the electrical generator is configured such that a harvesting rate is defined as an electrical power generation per movement of the bluff body and wherein the harvesting rate is varied throughout a range of oscillation amplitudes and is lower at small amplitudes than greater amplitudes; and further including a spring supporting the at least one bluff body for oscillation about a rest position, and wherein each bluff body is extending from the stand in a cantilevered fashion. 
 
     
     
       4. The fluid flow induced oscillating energy harvester according to  claim 3  wherein the harvesting rate is varied through at least one of i) varying a gap between a plurality of magnets of the electrical generator and associated coils of the electrical generator, ii) varying the magnet density of the electrical generator at varying amplitudes of the bluff body oscillation; iii) varying the coil density of the electrical generator at varying amplitudes of the bluff body oscillation; and iv) a rate of rotation generated in the electrical generator per oscillation displacement is higher at a higher amplitude of the oscillation of the at least one bluff body than at a lower amplitude of the oscillation of the at least one bluff body.